Process of making a piston ring

ABSTRACT

A CAST IRON PISTON RING IS PROVIDED WITH A FRACTION REDUCING PACKING OF BONDED IRON OXIDE AND CARBON POWDER IN A GROOVE OF ITS OUTER CIRCUMFERENTIAL FACE, AND WITH A HARD CHROMIUM ELECTRODEPOSIT ON ALL OTHER SURFACES BY FIRST APPLYING A PACKING COMPOSITION INCLUDING A HEAT CURING BONDING AGENT, THEREAFTER COATING THE PACKING WITH AN AQUEOUS POLYTETRAFLUOROETHYLENE DISPERSION, DRYING AND SINTERING THE RESIN INTO A CONTINUOUS FILM WHILE SIMUL-   TANEOUSLY CURING THE PACKING, AND THEREAFTER ELECTRODEPOSITING CHROMIUM, THE CURED PACKING BEING PROTECTED AGAINST ATTACK BY THE CHROMIUM PLATING BATH BY THE RESIN FILM.

March 27, 1973 mm. UMEZAWA 3,723,259

PROCESS OF MAKING A PISTON RING Original Filed NOV. 15, 1971 UnitedStates Patent 3,723,259 PROCESS OF MAKING A PISTON RING Kouji Umezawa,Konosu, Japan, assignor to Nippon Piston Ring Kabushiki Kaisha, Tokyo,Japan Original application Nov. 15, 1971, Ser. No. 88,320. Divided andthis application Feb. 22, 1972, Ser. No. 228,054

lint. Cl. C23b 5/48 U.S. Cl. 20415 3 Claims ABSTRACT OF THE DISCLOSURE Acast iron piston ring is provided with a friction reducing packing ofbonded iron oxide and carbon powder in a groove of its outercircumferential face, and with a hard chromium electrodeposit on allother surfaces by first applying a packing composition including a heatcuring bonding agent, thereafter coating the packing with an aqueouspolytetrafluoroethylene dispersion, drying and sintering the resin intoa continuous film while simultaneously curing the packing, andthereafter electrodepositing chromium, the cured packing being protectedagainst attack by the chromium plating bath by the resin film.

This is a division of application Ser. No. 88,320, filed on Nov. 15,1971, now Pat. No. 3,671,047.

This invention relates to piston rings suitable for automotiveinternal-combustion engines and to a process of making such pistonrings.

In its more specific spects, this invention relates to a piston ringcarrying an antifriction packing of bonded iron oxide (Fe 0.,) andcarbon powder mixture in a groove of the outer circumferential ringface.

Piston rings provided with such a packing have been found useful inreducing friction in a seal between the piston and the cooperatingcylinder at high compression ratios, and to retain its effectivenessafter extended service at high piston speeds. The known packings containwaterglass (aqueous sodium silicate) or a thermosetting resincomposition as a bonding agent, and require heat treatment at elevatedtemperature for curing the bonding agent.

It is also known to provide piston rings with chromium electrodepositsfor low friction and wear resistance, and it is common good practice todeposit chromium at a Vickers Pyramid Hardness of more than 700',preferably 850 to 1000. However, it has not been possible heretofore tomake a piston ring having both an outer circumferential packing of bakediron oxide and carbon while being covered with hard electrodepositedchromium on all or any other surface.

If the piston ring is chromium plated before receiving the ironoxide-carbon powder mixture, the hardness of the electrodeposit isreduced to about 650 VPH in the heat treatment. If the powder is appliedand baked prior to electrodeposition, the chromium plating solutioncorrodes the antifriction material and makes it unsuited for theintended purpose.

It is an object of this invention to provide a piston ring whichcombines the advantages of a bonded packing of the type described withthose of a hard chromium coating on at least one surface other than theouter circumferential surface of the piston ring.

Another object is the provision of a process of making such a pistonring.

It has now been found that the powder mixture may be coated prior toheat treatment with a fluoroplastic resin composition capable of beingheated to anadequate curing temperature for the powder mixture, ofwithstanding attack by the chromium plating bath, and of protecting thepacking, and that the heat treated piston ring may thereafter besubjected to chromium plating without attack on the cured packing. Thethin film of resin is an effective lubricant under the normal conditionsof piston ring use for at least the breaking-in period, and does notinterfere with the operation of the cured packing, nor shorten itsuseful life.

Other features and many of the attendant advantages of this inventionwill readily be appreciated as the same becomes better understood byreference to the following detailed description of a preferredembodiment when considered in connection with the appended drawing.

The sole figure of the drawing shows a piston ring prepared by theprocess of the invention in fragmentary section on its axis.

The body 1 of the ring consists of cast iron. It is of generallyrectangular cross section, the relatively narrow, outer circumferentialface 2 of the piston ring body being formed with a shallow annulargroove 3 extending over much of the axial height of the ring.

The groove 3 is filled with a packing 4 of bonded iron oxide and carbonpowder. The wide upper and lower radial faces 5, 6 of the piston ringbody 1, and the inner, circumferential face 7 are covered with a coating8 of electrodeposited chromium. A film 9 of polytetrafluoroethylene(TFB) covers the exposed face of the packing 4.

In an actual embodiment of the invention, the piston ring body 1 hadanouter diameter of 83 mm., an axial height of 1.9 mm., and a radialwidth of 3.4 mm. The groove 3 and the packing conformingly receivedtherein had cross-sectional dimensions of 0.5 mm. in the direction ofthe ring diameter, and 0.45 mm. in the direction of the piston ringaxis. The chromium electrodeposit 8 had a thickness of 8 microns, whilethe polytetrafluoroethylene film had a thickness of 55 microns in thefinished piston ring.

In producing the ring, the groove 3 was packed with the conventionalmixture of iron oxide, carbon, and waterglass bonding agent. A layer ofTFE powder dispersion containing a small amount of temporary binder inits aqueous medium was applied over the exposed portion of thecircumferential ring face 2 and the exposed face of the green packing 4,and the ring was thereafter slowly heated to evaporate the waterpresent, at about 200 C. in one hour, and thereafter simultaneously tocure the TFB layer which coalesced into a gel, and the powder mixture.The ultimate temperature was somewhat below 390 C. but above thesintering temperature for the TFB composition. The coated piston ringwas then cooled slowly to solidify the TFB layer into a continuous film.

It was next immersed in a chromium plating bath and made the cathode inthe bath until chromium was deposited to the average thickness indicatedabove. The bath, conventional in itself, 250 g./l. chromium trioxide,approximately 1.4 g./l. sulfuric acid, and 5.5 g./l. sodiumfluosilicate. Its temperature was 65:2" C. and the cathode currentdensity was controlled at 60 to amps./ dm.

Careful examination of a cross section showed that none of the chromiumplating solution had penetrated into the packing, and thus could notcause oxidation of the Fe O and the resulting loss of coherence whichcould cause the packing to be dislodged during service.

The piston ring prepared as described performed well inextended serviceunder taxing conditions.

While TFE is preferred at this time as a material for the fiuoroplasticfilm 9, the several other fluoroplastics now in commercial use,including polychlorotrifluoroethylene, fluorinated ethylene propylenepolymer, or polyvinylidene fluoride may be substituted with thenecessary 3 changes in processing conditions, particularly in thesintering temperature.

The thickness of the tluoroplastic film 9 may be chosen to suitrequirements, that is, adequately to protect the cured powder mixture,and the optimum value depends on variables relating both to the pistonring and to the cylinder in which the piston ring is to be used. Someexperimentation thus is unavoidable, but a thickness of approximately 50microns or more in the cured fluoroplastic and a corresponding thicknessof the applied dispersion will normally give good results. Similarconsiderations hold for the chromium electrodeposit, and those skilledin the art will modify the procedure outlined above to meet specificrequirements. A chromium layer less than 5 microns thick is rarelyadequate. The metal employed for the body portion of the ring mayrequire changes in the chromium thickness in an obvious manner.

It should be understood, therefore, that many modifications andvariations of the present invention are possible in the light of theabove teachings, and that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically described.

What is claimed is:

1. In a process of making a piston ring in which a piston ring bodyhaving an outer grooved, circumferential face is packed with a mixtureof iron oxide, carbon, and a bonding agent filling a groove in saidface, and said mixture is cured at elevated temperature, the improvementwhich comprises:

(a) coating the packed mixture prior to said curing with a layer of afiuoroplastic resin composition capable of being heated to said elevatedtemperature and responsive to said heating by forming a continuous filmof fluoroplastic resin;

(b) heating the piston ring body carrying said packing and said resincomposition to a temperature sufficient to cure said pacikng and toconvert said composition to said film; and

(c) thereafter making said piston ring body the cathode in a chromiumplating bath under conditions to deposit chromium having a VickersPyramid Hardness greater than 700 on another face of said body.

2. In a process as set forth in claim 1, said fluoroplastic resin beingpolytetrafiuoroethylene, polychlorotrifluoroethylene, fiuorinatedethylene propylene ploymer, or polyvinylidene fluoride.

3. In a process as set forth in claim 1, said fiuoroplastic resin beingpolytetrafluoroethylene.

References Cited UNITED STATES PATENTS 3,051,633 8/1962 Paull et al.204-25 X 3,683,477 8/1972 Sugahara 204l5X GERALD L. KAPLAN, PrimaryExaminer US. Cl. X.R. 20425, 29

